is it true that physical intimacy love between couples declines?

Falling in love is easy. Staying in love is the hard part. My mom once said that it's not about staying in love, it's about falling in love over and over again with the same person. There is a smart man named Dr. Hurley that explains why these feeling ebb and flow. You should do a search and check out his website. Read about the Love Bank, and how deposits and withdrawls effect how you feel about a person.

Not necessarily. It certainly doesn't have to if both people are committed and still in love with each other. I found it got better over the years.